1. Field of the Invention
The present invention relates to a telephone system used for an extension telephone system in an office, its log-in management method and a server device. More specifically, the invention relates to a telephone system for performing voice communications among terminals by using Internet Protocol (IP), its log-in management method and a server device.
2. Description of the Related Art
A system for communicating voice information via a best-effort communication network, such as the Internet, has been known. Such a system is referred to as an IP telephone system or Voice over IP (VoIP). This technology is also applied to a local communication network such as a private telephone network. Hereinafter, such a system is referred to as the IP telephone system, and a telephone set used for the system is referred to as an IP telephone set.
Even in a conventional telephone system, the multi-functionalization of the system has been advanced and a technique providing a fine service by combining a user's personal identification (ID) and a personal information database has been disclosed (for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-158771). Especially, with use of a protocol referred to as Session Initiation Protocol (SIP), a further development of the IP telephone system has been expected.
Such an IP telephone system associates IP telephone sets with telephone numbers and IP addresses, respectively, to create a database and integrally manages the IP telephone sets by a server device such as an exchange server. Thereby, the IP telephone system has a procedure, in which when a user starts using the IP telephone set, the IP telephone set notifies and resisters user identification information (telephone number and ID, etc.) together with the IP addresses to and in the server device. Since the identification information has not been stored in the IP telephone set yet at the initial state thereof, the user inputs the user identification information manually. The registration processing at the first time is specifically referred to as log-in. In general, the IP telephone set performs re-registration processing periodically (for instance, once at every hour or once at every day) to update the registered information after completing log-in processing.
In the meantime, in the telephone system like this, the user can log in freely from any IP telephone set usually. In other words, even any IP telephone set placed anywhere, the telephone number of the user is assigned to the IP telephone set when the user logs in thereby and the user can use the IP telephone set as their own. When the user moves their location, the user logs out from the IP telephone set which has been used by itself and logs in the system from the IP telephone set positioned at the moving destination after deleting the registered information thereform.
However, if the user moved while forgetting to log out from the telephone system, incoming calls to the user are subjected to connect with the IP telephone positioned at the former place, and it causes an inconvenience particularly in a place of a highly public nature, such as an office. To delete the registered information from the telephone system, the user has to return to the former place to log out thereform and feels it as a nuisance depending on circumstances.